In the prior art, closed-cell foam resins have been prepared from a mixture of a resin, a curing agent and a blowing agent, allowing the mixture to form a closed-celled foam, and thereafter curing the foamed product. Some of the closed-celled rigid foams in the prior art have substantial structural strength but are not porous to satisfy the requirements of the present invention. That is, there is no satisfactory way of impregnating the cells with the necessary filler material required for strengthening. In general, the foam materials in the prior art do not have both open cell structure and the rigidity necessary to provide products made therefrom with the necessary and desirable structural strength and stability required according to the invention.
In the prior art, when a crushing process has been applied to a fully cured rigid closed-cell foam, numerous problems have been encountered. For example, the material does not regain its original thickness and shape after the crushing technique is applied and the material sometimes crumbles and breaks.
A search of the patent literature discloses various foams and crushing processes. For example, U.S. Pat. No. 3,386,877 discloses a thermoplastic polyurethane in which a layer thereof is cooled and then crushed. The foam is flexible above the glass temperature to a sufficient degree to permit a desired degree of recovery after the foam has been crushed. A result is achieved by selectively varying the temperature of at least a first portion of a resinous foamed body, having a second order transition point and a plurality of closed cells having cell walls, to a temperature below its second order transition point (glass temperature) and compressing the body and rupturing cell walls of the first portion of the foam body while maintaining at least a second portion of the body above its second order transition point and not rupturing a major portion of the cell walls thereof.
In U.S. Pat. No. 3,709,843, flexible densified polyurethane foams are made for use as cushioning and rug padding. The flexible polyurethane is formed as a partially cured cellular material and then a compressive force is applied to the partially cured material to reduce its volume by a desired amount.
In U.S. Pat. No. 3,658,972, different densities of flexible polyurethane foam are achieved by allowing part of the foam to freely expand before cure is completed and then compressing the freely expanded portion. Thereafter the cure is completed.
U.S. Pat. No. 3,223,654, discloses a method for making a rigid epoxy foam.
The following patents disclose various polyurethane and polyepoxide foams.
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